The present invention relates to a pressure-reducing valve means for controlling the outflow of a fluid mixed with dust from a pressurized container. The pressurized container may be a cyclone so that it is intended that the exiting fluid includes dust entrained therein, or it may be a question of controlling the release of excess air from a container, the air being contaminated with dust.
To maintain the flow at the desired level, it may be necessary to slow it down. Normally, because of the dust admixture, it is then not possible to use conventional pressure-reducing valve means with movable parts, in part because of the inevitable wear of valve parts which would be caused by the entrained dust and in part because of the substantial risk that gaps and spaces in the valves can accumulate dust particles with the ensuing risk of a blocking of otherwise movable parts.